It's a much better time to be on the fantasy baseball waiver wire than last week due to the promotion of several top prospects (Keston Hiura, Austin Riley, Oscar Mercado) and the convincing excellence of veterans (Hunter Pence, Ryan Pressly). So, if you have holes in your roster heading into Week 8, now is the time to be aggressive with free agent adds.

We'll help sort through the available options to determine which players being widely added or (overlooked) are worth the trouble and which you might be best steering clear from. It's not an exact science, of course, but this should be a solid guide for navigating fantasy baseball free agents in the near-term.

Week 8 Fantasy Baseball Top Waiver Pickups

2B/3B Tommy La Stella, Angels (39.8 percent owned ) - It's difficult to understand exactly what's going on with La Stella, a career part-time player now likely bound for an All-Star bid. He's hitting .301 with 11 home runs and 25 RBIs in 38 games, which is approaching a large enough sample size to think this is at least somewhat for real. Plus, his batting average on balls in play is .245, meaning the lofty hitting numbers could last. It's still Tommy La Stella, though, so we'll be throwing our hands in the air in exasperation at this unforeseen production for at least a little while longer. At the very least, as long as he's hitting ahead of Mike Trout and Shohei Ohtani, he should score runs.

OF Franmil Reyes, Padres (36.4 percent owned) - We highlighted Reyes a couple of weeks ago in this column, and he's made us look good by raising his batting average from the low-.200s to .265 while continuing to mash home runs and, most important, play almost every day. He's 61 percent owned in Yahoo leagues but still grossly underowned on ESPN. If you need home runs or RBIs without sacrificing much in average or runs, this is your guy.

OF Hunter Pence, Rangers (29.3 percent owned) - Pence comes with credibility less accomplished players lack given his three All-Star appearances and long-time success at the plate. So, we're inclined to believe in his strong start to the year, which comes on the heels of a putrid 2018. As documented in The Athletic, Pence has made meaningful adjustments to his swing, and he's drawing walks more than ever before. His power is back, too, with seven home runs in 27 games. It might be worth riding this hot streak as long as it takes you -- and it might be a while considering the weather is about to heat up for him in one of baseball's best hitters parks.

2B Keston Hiura, Brewers (25.6 percent owned) - We wrote about Hiura's chance to win a long-term middle-infield job in Milwaukee now that Travis Shaw is on the IL. With that in mind, it's easy to see a scenario where the top prospect who hit at every level of the minor leagues can be an immediate multi-category fantasy asset for the rest of the season. The 22-year-old righty was hitting .333/.408/.698 with 11 HRs and four SBs at Triple-A this year. Pick him up if you can.

3B Austin Riley, Braves (20.4 percent owned) - Like Hiura, Riley is a top prospect who will likely surpass 50 percent ownership within a week if he begins his career well. He hit a home run in his first game, so that's a good start, and he could also get regular playing time moving forward until Ender Inciarte returns from the IL. Another 22-year-old righty, Riley had already mashed 15 homers this year at Triple-A.

OF Oscar Mercado, Indians (10.2 percent owned) -- The 24-year-old speedster was called up earlier this week, and if you're hurting for steals, he can help. Mercado had already swiped 14 bags at Triple-A this year, and over the past four minor league seasons, he's averaged 39.5 SBs in 123.5 games. Mercado isn't a great average hitter, but started taking more walks last season and has shown some pop, hitting as many as 13 HRs in a season. Even with the Indians desperate for outfield help, playing time is an issue, but Mercado has a lot of upside. -- Matt Lutovsky

3B Gio Urshela, Yankees (8.1 percent owned) - Urshela bears similarity to La Stella in terms of out-of-nowhere fantasy relevance, though his sample size is smaller. Miguel Andujar missing the rest of the season due to injury will help his chances of sticking in this lineup, but it's difficult to trust a career .243 hitter with little pop.

OF Willie Calhoun, Rangers (6.5 percent owned) -- With all the top prospects being called up, we had to get one post-hype guy in here. Calhoun was a popular sleeper target heading into last year's drafts, but the pint-sized slugger couldn't find his footing and languished at Triple-A most of the season. He started there this year, but after hitting .304/.416/.557, the 24-year-old lefty got the call up this week. Calhoun homered in each of his first two games, which is sure to draw some attention. At 5-8, 187 pounds and with a low strikeout rate, it doesn't make sense that Calhoun can pop homers with the best of them (32 HRs between Double-A, Triple-A and the majors in 2018), but he has that ability. Playing time is an issue in Texas, but Calhoun is worth an investment in deeper leagues. -- Matt Lutovsky

RP Diego Castillo, Rays (21.4 percent owned) -- Considering Jose Alvarado hasn't recorded a save since April 7 and Castillo has four since then, we feel confident saying Castillo is more the closer than Alvarado. So, why is Alvarado owned in 73.8-percent of ESPN leagues and Castillo in just 21.4? Sure, Alvarado has slightly better numbers and Castillo doesn't get all the saves in Tampa (Emilio Pagan is steals some from time to time), but it seems obvious the Rays prefer to use the lefty Alvarado in high-leverage spots earlier in games more often than not. You really can't count on anything predictable with the Tampa bullpen, but it's silly that Castillo is so lightly owned. -- Matt Lutovsky

SP Wade Miley, Astros (18.3 percent owned) - Is there a more boring pitcher in baseball right now? Probably not. But being on the Astros gives Miley a chance at a double-digit win total. Perhaps he'll keep his ERA low enough to mitigate his low strikeout rate, though at best he's a low-risk, low-reward option.

SP Corbin Martin, Astros (15.7 percent owned) - The consensus top-100 prospect shined in his MLB debut this past week, striking out nine in 5.1 innings. He gets the benefit of playing for Houston and carries much more upside than Miley. It would be nice to be able to wait out a couple of his starts to make sure he can handle the big league jump, but you're probably not going to have much time to snatch him up.

RP Ryan Pressly, Astros (15.4 percent owned) - Pressly hasn't given up a run this season, he's struck out more batters than he's pitched innings, and he's next in line for the closer's role behind Roberto Osuna. About 50 percent of owners still own Andrew Miller when they should be turning to the new setup king. It isn't that hard.

SP Tyler Mahle, Reds (6.1 percent owned) - Despite not recording a win yet this year, Mahle has made important strides on the mound. His walk rate is way down and his strikeout rate is up, meaning it might be time for the 24-year-old righty to make good on his promise. He's a solid buy-low option if you need pitching depth.

SP/RP Felix Pena, Angels (3.0 percent owned) -- Pena is an odd case. He works as a traditional starter and as the primary long reliever after an opener, and his advanced numbers (4.48 FIP, .229 BABIP) aren't quite as good as his standard (3.49 ERA, 0.96 WHIP). But he's sporting a fantastic 13.1-percent swinging-strike rate and only walking 1.9 batters per nine, so clearly there's arm talent here. He needs to cut down on the homers, but the 29-year-old righty could be on the verge of a breakout. Of course, his BABIP could normalize and he could keep giving up homers, making him useless, but most of his peripherals give us hope. -- Matt Lutovsky